Proper operation of a recombinant (valve regulated) sealed lead acid battery, is highly dependent on regulating the proper internal gas pressure within the battery container. A pressure relief valve is an important component to maintain this proper gas pressure. A properly functioning pressure relief valve regulates the gas pressure by releasing gas from the battery container through a vent, coupling the internal battery plenum to the ambient atmosphere, when a high internal threshold pressure is reached, and resealing the vent when the internal pressure drops to a second low threshold pressure. Failure of the pressure relief valve may cause catastrophic failure of the battery due to excessive loss of the battery fluid at an undersirable low pressure or an explosion due to excess gas pressure, depending upon the nature of the performance failure of the pressure relief valve. A properly operating relief valve should accurately release and reseal in its every expected position in which the cell battery operates in response to the high and low pressure thresholds.
Pressure relief valves are often constructed of a resilient hard rubber. Venting action by the pressure relief valve depends upon the valve having a pressure responsive movement, such as the flaring of a skirt member of the valve, in response to pressure above some high pressure threshold and an ability to reseal below at another lower pressure threshold. Such a pressure relief valve construction is disclosed in the U.S. Pat. No. 4,780,378. At high pressure the skirt member of the valve flares outwardly to prevent the build up of internal pressure in the battery, but as the pressure drops the skirt member is relaxed and returns to a sealed condition.
The movement of the valve can cause the valve to move in a manner which causes it to improperly reseat following pressure reduction after a pressure relief operation. The valve mechanism in such a case ceases to function at the designated release and reseal gas pressures. In some designs resealing may fail to occur altogether. The valve is normally constrained to remain in an operative position by elaborative mechanical structure such as disclosed in U.S. Pat. No. 4,780,378. This structural arrangement is typically expensive.